Field of the Invention
The present invention relates to a bend-insensitive GI (Graded Index) type multimode optical fiber.
Related Background Art
It is known that a multimode optical fiber (hereinafter referred to as MMF) has a transmission loss which is caused by its structure and is larger than that of a single-mode optical fiber (hereinafter referred to as SMF) for long-haul optical communication. On the other hand, the MMF is widely used for short-haul information transmission such as LAN (Local Area Network) because it is easy to establish fiber-fiber connection because of its low splice loss and it becomes feasible to readily construct a network by using an equipment with a low specification.
Particularly, the GI type MMF used for short-haul information transmission tends to have a larger bending loss because the core radius is larger and a propagating light distribution is wider than that in the SI (Step Index) type SMF. Then, for example, U.S. Pat. No. 7,787,731 (First Literature), U.S. Pat. No. 8,280,213 (Second Literature), and U.S. Pat. No. 8,428,410 (Third Literature) disclose the bend-insensitive GI type multimode optical fibers (hereinafter referred to as BI-MMF) having the bending loss reduced by providing a trench portion with the refractive index lower than those of a core portion and a cladding portion and with a small width, outside the core portion.